The invention relates to catalysts useful for olefin polymerization. In particular, the invention relates to catalysts based on organometallic complexes that incorporate annulated cyclopentadienyl ligands.
Ziegler-Natta catalysts are a mainstay for polyolefin manufacture, but single-site (metallocene and non-metallocene) catalysts represent the industry""s future. These catalysts are often more reactive than Ziegler-Natta catalysts, and they often produce polymers with improved physical properties.
Many single-site catalysts incorporate cyclopentadienyl, indenyl, or fluorenyl ligands (xe2x80x9cCp-like ligandsxe2x80x9d). Much less is known about the impact of using ligands in which the negative charge of the ligand is potentially more highly delocalized. On the other hand, annealing benzo or other unsaturation-containing rings onto the traditional Cp-like framework is a potentially powerful way to perturb and control catalyst performance compared with the performance of traditional metallocenes.
Precursors to a number of potential annulated cyclopentadienyl ligands are known. For example, Murata et al. (Tetrahedron Lett. (1975) 2287) reported the synthesis of a cyclopenta[cd]phenalenyl anion, and concluded from 1H NMR studies that the anion is symmetrical and highly delocalized. No transition metal complexes were made.
Cyclopentazulenyl ring systems have also been prepared. For example, Yoshida et al. (Tetrahedron Lett. 24 (1983) 4585; J. Am. Chem. Soc. 106 (1984) 6383) concluded from 1H and 13C NMR studies that the negative charge in the cyclopent[e]azulenyl anion is highly delocalized. No transition metal complexes were made.
Hafner et al (Tetrahedron Left. 26 (1985) 2567) synthesized some cyclopent[f]azulenyl monoanions by reacting the parent compounds with n-butyllithium. Interestingly, a second mole of n-butyllithium adds to the fulvene moiety (the 4-position) of the anion to generate a monoalkylated, dianion: 
Hafner did not report organometallic complexes made from either the monoanions or the dianions. Complexes from monoanionic cyclopent[e]- and cyclopent[f]azulenyl ligands would be of considerable theoretical interest because of the potential for fluxional behavior. With two degenerate coordination sites, the complexes might undergo haptotropic rearrangements in which a metal migrates from one Cp ring to another to form a different complex that is its energetic equal.
Synthetic routes to cyclopent[a]azulenes and cyclopent[cd]azulenes have also been reported (see, e.g., Yasunami et al., Bull. Chem. Soc. Jpn. 66 (1993) 2273; 65 (1992) 2131; Hafner et al., Angew. Chem., Int. Ed. Engl. 13 (1974) 204; Liebigs Ann. Chem. 624 (1959) 37), but organometallic complexes from these and other cyclopentazulenyl ligand precursors are generally unknown. The cyclopent[cd]azulenes lack an acidic hydrogen.
Benzazulenes represent yet another kind of annulated cyclopentadienyl precursor that has not been used for transition metal catalysts. For example, Boekelheide et al. (J. Am. Chem. Soc. 88 (1966) 3950) reported the synthesis of 2H-benz[cd]azulenes starting from acenaphthenes. Deprotonation of benz[cd]azulenes should generate a an annulated cyclopentadienyl ligand, but this was not attempted by the authors.
Other benzazulenesxe2x80x94including benz[a]azulene, benz[e]azulene, and benz[f]azulenexe2x80x94have been synthesized, but these compounds lack an acidic hydrogen, and they have apparently not been used as ligand precursors for transition metal complexes. On the other hand, the compounds have a fulvene unit and are potential xe2x80x9cannulated cyclopentadienylsxe2x80x9d via nucleophilic addition.
Still other classes of compounds that lack an acidic hydrogen but are convertable to annulated cyclopentadienyl ligands include cyclopentaheptalenes or xe2x80x9caceheptylenesxe2x80x9d (see, e.g., Hafner et al., Pure Appl. Chem. 28 (1971) 153; Angew. Chem., Int.Ed. Engl. 15 (1976) 107), fluoranthenes, and acenaphthylenes. Transition metal complexes have not been reported.
Azulenes in general have seldom been used in making single-site catalysts, probably because they can be challenging to synthesize. However, a simple synthesis (suitable for use by students) of the parent compound has been reported (J. Chem. Educ. 65 (1988) 923) based on a route developed by Copland et al. (Tetrahedron Lett. (1977) 639.)
Nucleophilic addition of alkyllithiums to the fulvene system of azulenes is known as part of a three-step way to make 4-alkylazulenes (see Liebigs Ann. Chem. 650 (1961) 35). A similar nucleophilic addition was used by Sugano et al. (see, e.g., U.S. Pat. No. 6,344,530) in a multistep preparation of olefin polymerization catalysts that incorporate bridged bis(4-hydroazulenyl) complexes. In a representative example, phenyllithium adds to a 2-alkylazulene to generate a Cp-like anion, which reacts with 0.5 equivalents of dichlorodimethylsilane to give a dimethylsilyl-bridged bis(azulene). In a second step, double deprotonation followed by combination of the dianion with zirconium tetrachloride gives a bridged complex (see the ""530 patent at col. 57-58).
The polyolefins industry continues to need new polymerization catalysts. In particular, the industry needs catalysts having activities that are as good or better than the activities of single-site catalysts based on cyclopentadienyl, indenyl, and fluorenyl ligands. A valuable catalyst would incorporate ligands that can stabilize a cationically active site (as a Cp-like ligand does) without sacrificing much reactivity toward olefin monomers. Ideally, the catalysts could be made economically using well-established synthetic routes.
The invention is a catalyst system useful for polymerizing olefins. The catalyst system comprises an activator and an organometallic complex. The complex incorporates a Group 3-10 transition metal and an annulated cyclopentadienyl ligand that is pi-bonded to the metal. In particular, the annulated cyclopentadienyl ligand is a cyclopentazulenyl, benzazulenyl, cyclopentaheptalenyl, fluoranthenyl, acenaphthylenyl, or cyclopentaphenalenyl ligand. Molecular modeling studies reveal that organometallic complexes incorporating such annulated cyclopentadienyl ligands, when combined with an activator such as MAO, should actively polymerize olefins.
The invention includes a one-pot method for making organometallic complexes useful for olefin polymerization catalysis. The method comprises reacting a fulvene precursor with an organolithium, -sodium, -potassium, -magnesium, or -aluminum compound to produce a monoalkylated or monoarylated anionic adduct having a cyclopentadienyl moiety. Once generated, the anion is combined in the same reactor with a transition metal source to produce the organometallic complex. The invention also includes bimetallic complexes from cyclopentazulenes and a one-pot method for making them.